Boreal forests nowadays act as a sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to weather conditions and, specifically to ongoing climate warming. Extreme weather events such as heavy rainfalls or, conversely, heat waves during the growing season might perturb the ecosystem carbon balance and convert them to an additional CO₂ source. Thus, there is an urgent need to revise ecosystem carbon fluxes in vast Siberian taiga ecosystems as influenced by extreme weather events. In this study, we focused on the soil CO₂ pulses appearing after the rainfall events and quantification of their input to the seasonal cumulative CO₂ efflux in the boreal forests in Central Siberia. Seasonal measurements of soil CO₂ fluxes (both soil respiration and net soil exchange) were conducted during three consecutive frost-free seasons using the dynamic chamber method. Seasonal dynamics of net soil exchange fluxes demonstrated positive values, reflecting that soil respiration rates exceeded CO₂ uptake in the forest floor vegetation layer. Moreover, the heavy rains caused a rapid pulse of soil emissions and, as a consequence, the release of additional amounts of CO₂ from the soil into the atmosphere. A single rain event may cause a 5–11-fold increase of the NSE flux compared to the pre-rainfall values. The input of CO₂ pulses to the seasonal cumulative efflux varied from near zero to 39% depending on precipitation patterns of a particular season. These findings emphasize the critical need for more frequent measurements of soil CO₂ fluxes throughout the growing season which capture the CO₂ pulses induced by rain events. This approach has inevitable importance for the accurate assessment of seasonal CO₂ soil emissions and adequate predictions of response of boreal pine forests to climatic changes.

Boreal forest ecosystems are regions vulnerable to climate change. Such areas act as the main atmospheric carbon sinks in the world. Wildfires are among the drivers of ecosystem modification and functioning. Boreal wildfires emit an annual average of about 10% of global fire emissions. Taking into account recent climate warming and increases in the frequency of wildfires, boreal forests might switch their functional role from carbon sink to an additional source of atmospheric carbon. Soil respiration is the second largest component of the global carbon cycle and is highly sensitive to disturbance factors, including wildfires. To study the effect of wildfires on soil CO₂ emission rates, the fire chronosequence was investigated. During the first few years following the fire, the soil CO₂ emission rates were lower compared with the usual levels. It was found that 23 years after a fire, the site demonstrated transition behavior in soil emission rates between disturbed and completely recovered areas. The emission rates at the earliest successional stages are mainly controlled by soil moisture during the summer period. For the other successional stages, soil temperature had a huge impact on soil emission.

An understanding of how boreal forest composition responds to global environmental changes is an important challenge to predicting the future global carbon balance. Boreal forests are the most significant sink for atmospheric carbon dioxide; however, their sequestration capacity is highly sensitive to ongoing climate changes. The combination of the hydrothermal conditions of a territory strongly regulates its biogeochemical processes. The carbon fluxes in boreal forests are strongly mediated by the ground vegetation cover, composed of mosses (mesic) and lichens (xeric). Despite the concurrence of xeric and mesic vegetation types, their responses to climate variations varies significantly. Soil emission is an informative indicator of ecosystem functioning. In this study, we focused on the soil CO₂ dynamics during frost-free seasons with different precipitation regimes in the xeric and mesic boreal ecosystems of Central Siberia. Seasonal measurements of soil CO₂ emissions were conducted during frost-free seasons using the dynamic chamber method. Our findings reveal that the precipitation regimes of each year may control the seasonal soil emission dynamics. The soil moisture is the most important driver of emissions growth in the water-limited lichen pine forest (R²adj. = 18%). The soil temperature plays the largest role in the feather moss pine forest during the dry (R²adj. = 31%) seasons, and in the lichen pine forest during the wet (R²adj. = 41%) seasons. The cumulative efflux for the xeric and mesic sites is mostly related to the hydrothermal conditions, and not to the differences in ground vegetation cover. During the dry seasons, on average, the soil CO₂ emissions are 45% lower than during the wet seasons for both sites. These findings emphasize the need for estimating and including the hydrothermal characteristics of the growing season for detailed emission assessments.

Background The soils of the boreal zone contain significant reserves of carbon, therefore, their response to current climate changes will significantly affect the sustainability of forest ecosystems and the future concentration of CO 2 in the atmosphere. When modeling soil emission, it is necessary to focus on the main soil environment factors. In this paper, a simple exponential model of the soil CO 2 emissions growth was modified by introducing an additional parameter - the threshold soil moisture in different types of ecosystems based on the direct measurements. Results The developed model adequately reflects the dynamic changes in soil emission for different types of ecosystems. This result was achieved by including moisture as a second environmental factor besides temperature, describing changes in soil CO 2 emissions during the summer period. The error of direct measurements for all measuring seasons was about 20% of the values of direct measurements of the CO 2 flux. Note that such a high error was observed once per season in early and mid-June, reaching 60-80% on some days. Our models demonstrate in the season with the highest amount of precipitation the smallest differences in modeled fluxes about 15-20%, which indirectly indicates that the emission flux is not inhibited by insufficient moisture in this season. Conclusions The final model application depends on the characteristics of the microclimatic conditions of a particular ecosystem, namely, a factor that has a limiting effect on the biological processes. When studying the functional role of boreal forest ecosystems the moisture conditions consideration is crucial to explain the atmospheric CO 2 emission processes.

Boreal forests are sensitive to external factors, and even small variations can completely alter their natural carbon (C) balance. Today, we face not only the consequences of climate change but also intensified human activity. In most cases, forest disturbances decrease ecosystem stability by disrupting key structural components, often transforming ecosystems into C sources. Soil CO₂ efflux is a critical indicator of recovery following disturbances. This study explored the impact of different disturbance types (clear-cutting alone, wildfire alone, and both) on soil CO₂ efflux for various ground-cover vegetation (lichens, green mosses, and Sphagnum mosses) in Scots pine forests of the Siberian central taiga. The data indicate that changes in soil CO₂ efflux are predominantly driven by wildfires in lichen-dominated plots, by clear-cutting in green moss-dominated plots, and by both wildfires and clear-cutting in Sphagnum moss-dominated plots. Soil CO₂ efflux was reduced by 75% and 40% in lichen- and Sphagnum moss-dominated plots, respectively, across burned sites compared to the undisturbed site. The impact of clear-cutting is observed in a decline of the emission rates of from 40 to 60% compared to the undisturbed site for lichen- and moss-dominated plots. The interactive effect of wildfire and logging is established in the reduction of the emission rates, and this decline depends on the type of ground cover. This finding highlights the substantial impact of wildfires and clear-cutting on the C dynamics of Siberian boreal ecosystems. The diurnal and seasonal variations in soil CO₂ efflux were most pronounced for moss-dominated plots at disturbed sites. The main factors determining emission efflux variations are carbon content, type of ground cover, and forest floor thickness. This study contributes to a better quantitative understanding of soil CO₂ efflux in boreal Scots pine forests from the differently disturbed areas.

Forest ecosystems of the boreal zone are the most vulnerable areas in terms of current climate change. CO₂ fluxes from the soil surface are also significantly modified by sudden changes in environmental conditions. The main objective of this study was to trace the response of emission and exchange fluxes of CO₂ from the soil surface in mid-taiga ecosystems to changes in moisture conditions during heavy precipitation. Direct chamber measurement methods during the frost-free period of the year were chosen as the research methods. It was found that for pine stands with different ground cover, microclimatic characteristics make a significant contribution to the formation of the CO₂ flux. CO₂ pulses in the ecosystem of the lichen pine forest throughout the season are manifested in an increase in the exchange CO₂ CO₂ by an average of 3–4 times. In a green moss pine forest, the value of CO₂ pulses varies considerably during the season, reaching a maximum in the middle of the growing season: initial CO₂ flux rates increased 5 times. With an increase in the amount of precipitation in the lichen pine forest, an intensification of production activity by 12% was also observed. At the same time, the optimal soil moisture for producing the maximum amount of CO₂ for lichen pine forests is on average 33%, and for green moss pine forests it is about 46%.